1. Field of the Invention
The present invention relates to receiving apparatuses that receive, for example, broadcast waves.
2. Description of the Related Art
In recent years, various kinds of communication terminals, as typified by a cellular phone, that have functions for receiving broadcast waves of FM radio, digital radio or television have become widely used.
The electrical length of an antenna of a communication terminal for receiving, for example, FM broadcast waves are typically 3 m or so. Therefore, the size of the antenna is very large compared with the size of the body of the communication terminal for receiving FM broadcast waves. In contrast, the bodies of the receiving terminals for receiving broadcast waves have been becoming thinner and more reduced in size year by year.
One effective means for solving this unbalanced relation between the size of the antenna and the size of the body of the communication terminal is an adjunct cable, which is attached to the body of the communication terminal and equipped with an antenna function, as typified by an earphone antenna. An representative example of such an earphone antenna is disclosed in Japanese Patent No. 4123262.
In receiving broadcast waves, how a received high frequency signal is separated from an audio signal and a power signal that are transmitted through the adjunct cable is very important. If the frequencies of these signals are lower than several kHz, the problem is solved by preparing a new cable and connector pins. However, if the frequencies are several hundred MHz or more, the signals leak from their original cables to other cables owing to capacitive coupling among the original cables, resulting in the increase of transmission losses of the signals.
In the above Japanese patent, this problem is solved by disposing a high-frequency cutoff circuit on the earphone antenna or on the receiving terminal, that is, by employing a technology to separate overlapped signals with the use of frequency differences among signals.